1. Field of the Invention
The present invention relates to a process for the hydrogenation of sugars and sugar mixtures to sugar alcohols or sugar alcohol mixtures wherein the sugars or sugar mixtures are hydrogenated with hydrogen in an aqueous solution at elevated temperature and elevated pressure by using a catalyst.
2. Description of the Related Art
EP 0 152 779 B1 describes a process for manufacturing a mixture of 1-0-.alpha.-D-glocupyranosil-D-mannite (hereafter called 1,1-GPM) and 6-0-.alpha.-D-glocupyranosil-D-sorbite (hereafter called 1,6-GPS) from 6-0-.alpha.-D-glocupyranosil-D-fructose (isomaltulose, palatinose.sup.R). In the described process, isomaltulose is hydrogenated continuously at elevated pressure and elevated temperature in a fixed-bed process by using catalysts taken from the eighth subgroup of the periodic system, in particular nickel, cobalt and iron. The process described above produces 1,6-GPS and 1,1-GPM with a ratio of approximately 1:1.
Another process for producing 1,6-GPS and 1,1-GPM from isomaltulose is known from DE 44 16 115 A1. Here, the catalyst described in EP 0 152 779 B1 contains additional elements from the sixth subgroup of the periodic system. This process also produces 1,6-GPS and 1,1-GPM with a ratio of about 1:1. DE 44 16 408 A1 and DE 39 34 457 A1 also describe processes for the hydrogenation of sugars, for example of glucose, xylose, lactulose or maltose. The catalysts employed in the hydrogenation reaction are carrier-free formed bodies made from elements of the eighth and sixth subgroup of the periodic system.
If stereo-isomers (epimers) can be formed by hydrogenating an educt, such as isomaltulose, then it is possible to adjust the stereo-selectivity of the reaction such that the reaction products are formed with a predetermined ratio. It is therefore desirable to develop a process for certain applications which produces reaction products with a predetermined ratio which could hitherto not be attained. It is also desirable to improve the process flow, the handling of the catalysts and the process costs of the conventional processes.